1. Technical Field
The present disclosure concerns a rotor blade and a rotor blade element for a wind power installation, the rotor blade itself and production processes for the rotor blade element and the rotor blade, including repair processes.
2. Description of the Related Art
Rotor blades for wind power installations have long been known and described for example in DE 10 2004 007 487 A1 and DE 103 19 246 A1. In operation thereof, they are subjected to high levels of loading due to wind pressure, erosion, temperature fluctuations, UV “Ultraviolet” irradiation and precipitation. At the same time the rotor blades however should be as light as possible to keep down the flexural loads acting on a rotor blade hub which is possibly provided, as well as the associated bearings and the pylon of the wind power installation. It has proven to be desirable to produce rotor blades from individual elements and to interconnect those elements to form a hollow chamber-like rotor blade. The rotor blade elements used are usually a rotor blade pressure side, a rotor blade suction side and one or more connecting limbs for connecting and stiffening the rotor blade pressure and suction sides. It has also proven desirable for the rotor blade pressure side and the rotor blade suction side to be produced in one piece and in that production to already arrange limbs at their required locations.
Rotor blades and rotor blade elements are usually produced in a shaping process in which fiber materials and/or core materials, in particular balsa wood, are introduced into a rotor blade element mold and acted upon with a hardening resin to form a composite material which can be subjected to loadings in the above-indicated sense. In that respect it is desirable for the resin to be used as an infusion resin in a vacuum infusion process. Production processes for such composite elements are described, for example, in DE 103 44 379 A1, the content of which is entirely incorporated into this description by reference thereto. In such an infusion process a mold release agent, for example a mold release film or a separating agent, is firstly introduced into a production mold. Fiber materials, for example glass fiber layers, are deposited thereon, and covered with a vacuum film. The vacuum film is sealed off along the edges of the production mold. A reduced pressure, sometimes also referred as a “vacuum”, is produced between the vacuum film and the production mold by sucking air out of the fiber material. At the same time a hardenable infusion resin is sucked from a supply into the region subjected to the reduced pressure in order to impregnate the fiber material and to be uniformly distributed therein. In that respect particular care must be taken to ensure that the fiber material is impregnated as completely as possible to avoid stability-reducing gas inclusions and micropores. The attempt is usually made to promote uniform impregnation of the fiber material with the infusion resin through a plurality of feed conduits for the hardenable infusion resin. The hardenable infusion resin is also subjected to a hardening reaction in the production mold in order to combine with the fiber material to afford a strong composite element. Optionally the composite element can be further hardened after removal from the production mold.
A disadvantage with known shaping processes like that described hereinbefore is that particular precautions have to be taken for removal of the molding from the mold in order to prevent the hardened composite element from adhering to the mold or to permit detachment of the composite element from the mold without serious damage to the surface of the molded composite element. Prior to the present invention, for example, mold release coatings had to be used for that purpose on the molds employed and/or the molds had to be lined prior to insertion of the fiber material with a mold release film or the like which after the molding operation had to be detached from the molded composite element and disposed of Mold release films and the use thereof are described for example in the handbook “Faserverbundbauweisen: Fertigungsverfahren mit duroplastischer Matrix”, Springer Verlay, 1999, under the keyword “Trennfolien”. In addition, films are required as vacuum films. Those films cover the fiber material and prevent the entry of air during the hardening resin infusion step. The vacuum films also had to be removed from the rotor blade or rotor blade element after the infusion procedure. In addition, a composite element produced in the vacuum infusion process has micropores at its surface and in its interior. In particular micropores at the surface of a rotor blade or rotor blade element are detrimental as they produce unevennesses which can form attack locations for weather influences and thus reduce the durability of the surface. Similarly, micropores in the interior of a rotor blade element or a rotor blade can also reduce the durability and/or stability of the rotor blade or rotor blade element. It is therefore frequently necessary to close micropores by a pore filler before the hardenable infusion resin has completely hardened. It is also frequently necessary to post-work the surface to close micropores arranged there.
To form a surface which is as durable as possible and resistant to weather influences and erosion, the attempt has been made to use a surface layer with a gel coat process as described in DE 103 44 379 A1. A disadvantage in that respect is that with such a process it is necessary to observe a maximum processing time until the gel coat mixture has fully reacted to such an extent that it can be coated with fiber material. That leads to an unwanted reduction in the speed of the production process for a rotor blade or rotor blade element. In addition, after introduction of the gel coat mixture further operation must be implemented without delay to permit reaction of the infusion resin with the partially hardened gel coat mixture. If the waiting period after expiry of the pot time is excessively long then the infusion resin and the gel coat surface layer are not sufficiently joined together so that the durability of the rotor blade element or rotor blade produced in that way is reduced. It is therefore not possible to interrupt the production of a rotor blade element or rotor blade just as desired when using a gel coat process; the production of a rotor blade element or rotor blade thus becomes undesirably inflexible. There is also the disadvantage that, depending on the gel coat mixture employed, the choice of the mold release agent is limited. If the mold release agent and the gel coat mixture are not compatible with each other, surface flaws are formed. In addition, in production of a gel coat mixture it is not possible to exclude the possibility that the constituents thereof are inadequately mixed. That results in an unevenly structured surface with flaws, at which, for example, a paint or lacquer cannot sufficiently adhere. Such flaws have to be dressed by hand which is a complicated and expensive procedure to avoid the early occurrence of paint detachment phenomena. Added to that is the fact that the gel coat mixtures are fluid so that upon being introduced into the production mold they have a tendency to flow down therein. To ensure a thickness, which is adequate at every location, for a surface layer produced using the gel coat process, it is therefore necessary to use an excess of gel coat mixture. However a surface layer produced using the gel coat process cannot be of uniform thickness at every location on a rotor blade or rotor blade element.
The above-mentioned production processes are highly time-consuming and cause environmental pollution due to the materials used therein, in particular the surface coatings and the mold release films which are used as disposable articles. Moreover post-treatment of the surface of the composite element is frequently necessary, in particular the surface of a rotor blade or rotor blade element, to level out for example surface edges and grooves caused by mold release films or to repair surface damage which occurs upon removal of the composite element from a mold with a faulty mold release layer. Residues of the mold release agent on the surface of a rotor blade or rotor blade element, which can occur particularly when using mold release coatings instead of mold release films, also have to be removed by hand in a complicated and expensive procedure and the resulting surface flaws have to be repaired.